1. Field of the Invention
The present invention relates to a chemical supply system that supplies a chemical solution by using a chemical supply pump performing suction and discharge of the chemical solution by volume changes inside the pump chamber.
2. Description of the Related Art
In a process using a chemical solution in a semiconductor fabrication apparatus, a chemical supply system such as described in Japanese Patent Application Publication No. 2006-46284 has been suggested for coating a chemical solution such as a photoresist solution in predetermined amounts on a semiconductor wafer.
In the chemical supply system described in Japanese Patent Application Publication No. 2006-46284, a chemical supply pump is provided for sucking the chemical solution contained in a chemical tank and coating the chemical solution that has been sucked in on a semiconductor wafer in predetermined amounts. More specifically, the chemical supply pump has a diaphragm partitioning a pump chamber that is filled with the chemical solution and a working chamber through which working air flows, and is configured such that the air is supplied from a regulator into the working chamber, the diaphragm is deformed toward the pump chamber, and the chemical solution is discharged. Further, a vacuum source is connected to the chemical supply pump, and by supplying a negative pressure from the vacuum source to the chemical supply pump, the volume of the pump chamber is increased and the chemical solution is sucked in.
The level of the chemical solution contained in the chemical tank varies as the chemical solution is discharged and a hydraulic head pressure inside the chemical tank changes accordingly. For example, when the hydraulic head pressure has varied significantly, the suction time during suction of the chemical solution into the chemical supply pump varies significantly. As a result, the time required to suck the chemical solution into the chemical supply pump can change significantly.
In order to resolve this problem, a configuration can be considered in which a liquid level sensor or a weight sensor is provided in the chemical tank, the variation of hydraulic head pressure is directly detected, and the suction operation in the chemical supply pump is controlled according to the detection result. However, in such a configuration, the system should be changed on both the chemical tank side and the chemical supply pump side, and the number of changes required for the already existing systems is large.
Further, a configuration can be also considered in which a needle valve is provided at a position on the chemical tank side, rather than the chemical supply pump side, a throttle amount is manually adjusted, and the effect of hydraulic head pressure is reduced, but in this case the effect of hydraulic head pressure cannot be reduced automatically.